Generally, an area of an imaging device used for a so-called compact digital camera is smaller than that of an imaging device used in a single-lens reflex digital camera, or is smaller than an exposure area of a silver-salt film used in a single-lens reflex camera. Thus, a focal distance of the compact digital camera is shorter than that of the single-lens reflex digital camera or the single-lens reflex camera, when the focal distances of photographic optical systems thereof necessary for photographing an image having the same angle of field are compared with each other. In addition, when an F-number of each of the photographic optical systems is set to be constant, a depth of field of the photographic optical system having the shorter focal distance becomes deeper than that of the photographic optical system having the longer focal distance. In other words, the compact camera generally has a characteristic of a deep depth of field.
It is possible to make the depth of field shallow, if the F-number can be made smaller as the focal length becomes shorter. However, a diameter of the photographic optical system must be enlarged when the F-number is to be made small, which is not suitable for the compact camera since size and costs are increased. Thus, the compact digital camera has a characteristic in which a focused state is obtained for a relatively wide distance range. Such a characteristic is advantageous in that an image having reduced blur is obtained in a case where a photographic object of the same brightness is photographed, although the characteristic becomes disadvantageous when photographing is performed in which the background is blurred largely such as in portrait photographing, i.e., an image having large blurring is difficult to obtain.
In order to deal with the characteristic of the compact digital camera, for example, Japanese patent application publication No. H11-266388, No. 2003-37767, No. 2003-101858, and No. H09-318870 each proposes a camera which blurs a background image by utilizing image processing. The camera proposed in each of the publications changes a characteristic of a filter in the image processing according to a distance between a photographic object and the camera, or according to a position of a photographic object in an angle of field, so as to realize blurring having perspective.